The present invention relates to a servo controller and a method for controlling a servo. More particularly, it relates to a servo controller that controls an embedded servo by providing servo sections in a data recording surface of a recording medium, such as a magnetic disk.
FIG. 1 is a schematic block diagram of a prior art servo controller 50. The servo controller 50 reads data from a recording medium, such as a magnetic disk.
The servo controller 50 includes an automatic gain control (AGC) circuit 1, a D/A converter 2, a filter circuit 3, an A/D converter 4, a servo processing circuit 5, and an AGC circuit controller 6.
The AGC circuit 1 receives an input signal IN, which includes data read by a recording medium by a read head (not shown). The AGC circuit 1 sets its gain based on an AGC voltage SG1 supplied from the D/A converter 2, amplifies the input signal IN based on the gain, and sends an amplified data signal SG2 to the filter circuit 3.
The filter circuit 3, including a low-pass filter, eliminates unnecessary high frequency components in the amplified data signal SG2 so to generate a filtered signal SG3, and provides the filtered signal SG3 to the A/D converter 4. The A/D converter 4 converts the filtered data signal SG3 to a digital data signal SG4, and provides the digital data signal SG4 to the servo processing circuit 5 and the AGC circuit controller 6.
The servo processing circuit 5 servo-controls the read position of the read head based on the digital data signal SG4. The servo processing circuit 5 includes a discrete Fourier transform (DFT) operational circuit (not shown). The DFT operational circuit performs a discrete Fourier transform on the digital data signal SG4 to generate phase data PD. The phase data PD is used to servo-control the read position of the read head.
In addition to the digital data signal SG4, the AGC circuit controller 6 is provided with a target value PA, which is pre-stored in a register, or the like. The target value PA generates the filtered data signal SG3 so that its amplitude is substantially equal to the full-scale range of the input level of the A/D converter 4. The AGC circuit controller 6 compares the digital data signal SG4 and the target value PA, integrates the error component to generate an integral signal SG5, and sends the integral signal SG5 to the D/A converter 2.
The D/A converter 2 converts the integral signal SG5 to an analog signal, and provides the AGC circuit 1 with the AGC voltage SG1.
The A/D converter 4, the servo processing circuit 5, and the AGC circuit controller 6 are operated in accordance with a clock signal CLK, which is generated by a PLL circuit.
Servo sections are locally defined in each track of a recording medium, such as a magnetic disk. FIG. 2 illustrates one of the servo sections. The servo section includes an R/W recovery segment 7, a servo mark segment 8, an AGC segment 9, and a phase detection segment 10. FIG. 3 is a diagram illustrating the waveform of the signal IN in the servo section. Although the signal IN of the servo section actually has a Lorentz waveform, the signal IN is illustrated as having a sin wave for the sake of brevity.
With reference to FIG. 3, when the servo section is read, the R/W recovery segment 7 is read during a first time period t1. The signal IN has a predetermined amplitude and frequency during the first time period t1. Then, the servo mark segment 8 is read during a second time period t2. The signal IN has a continuous null level during the second time period t2.
In comparison to the R/W recovery segment 7, the signal IN has a lower frequency and a greater amplitude when the AGC segment 9 is read during a third time period t3. When the phase detection segment 10 is read during a fourth time period t4, the frequency and amplitude of the signal IN are the same as the frequency and amplitude of the signal IN when the AGC segment 9 is read.
FIG. 4 is a combined timing and waveform chart of the AGC voltage SG1 when the servo section is read.
When the read head starts reading the R/W recovery segment 7, the AGC circuit controller 6 calculates the error between the digital data signal SG4, which corresponds to the input signal IN, and the target value PA. Based on the digital integral signal SG5 generated by the AGC circuit controller 6, the D/A converter 2 supplies the AGC circuit 1 with the AGC voltage SG1.
If the amplitude of the input signal IN of the R/W recovery segment 7 is small and the error between the digital data signal SG4 and the target value PA is large, the level of the AGC voltage SG1 increases. As a result, the digital data signal SG4 becomes the target value PA.
When the servo mark segment 8 is read and the input signal IN has a continuous null level, the digital data signal SG4 is accordingly generated at a continuous, null level. This fixes the integral signal SG5 and the AGC voltage SG1.
Then, when the reading of the AGC segment 9 is started, the error between the digital data signal SG4, which corresponds to the input signal IN, and the target value PA is recalculated by the AGC circuit controller 6. The D/A converter 2 then supplies the AGC circuit 1 with the AGC voltage SG1 in accordance with the integral signal SG5 of the D/A converter 2.
When the reading shifts from the servo mark segment 8 to the AGC segment 9, the amplitude of the read signal IN becomes greater than that when the R/W recovery segment 7 is read. Thus, the amplitude of the filtered data signal SG3, which is generated by the filter circuit 3, exceeds a target value.
As a result, the AGC circuit controller 6 gradually decreases the AGC voltage SG1 until the digital signal SG4 converges to the target value PA. In a state in which the amplitude of the filtered data signal SG3 is substantially equal to the full-scale range of the A/D converter 4, the reading of the phase detection segment 10 is started.
The signal IN has the same frequency and amplitude when the phase detection segment 10 and the AGC segment 9 are read. Thus, the phase detection segment 10 is read in a state in which the A/D converter 4 is provided from the beginning with the substantially full-scale range, filtered data signal SG3. Thus, the reading of the phase information stored in the phase detection segment 10 is guaranteed, and servo-control, which corrects the read position, is immediately performed.
In this manner, the servo controller 50 amplifies the input signal IN, which corresponds to the data read from the recording medium. The servo controller 50 then extracts the filtered data signal SG3, including a fundamental wave from the amplified data signal SG2. Further, the servo controller 50 performs the discrete Fourier transform on the digital data signal SG4, which is the converted filtered data signal SG3, to obtain the phase data PD. Based on the phase data PD, the servo controller 50 performs phase servo to position the read head.
However, when the servo section is read, the AGC voltage SG1 is shifted whenever the read segment is changed to provide the A/D converter 4 with the substantially, full-range filtered data signal SG3. Therefore, whenever the read segment of the servo section changes, time is required for the amplitude of the filtered data signal SG3 to substantially converge to the full-scale range input level of the A/D converter 4. As a result, it is difficult to compress the servo section and shorten the read time.
When starting the reading of the phase detection segment 10, to provide the A/D converter 4 with the substantially, full-scale range filtered data signal SG3 from the beginning, the AGC segment 9 must have a sufficient amount of sample data and data storage space.
Further, as the density and reading speed of the recording medium increase, the high-speed rotation of the recording medium causes the input signal IN provided to the servo controller 50 to have a relatively high frequency. Thus, the AGC circuit 1, the filter circuit 3, and the D/A converter 2, all of which are analog circuits, must be adaptable to the relatively high frequency. However, an analog circuit adaptable to a high frequency is complicated. Consequently, the manufacture of such a circuit is difficult. Further, to decrease power consumption and prevent the temperature of the device from becoming excessively high, the power supply voltage must be low. However, a low power supply voltage renders phase calculation of the servo controller 50 to be susceptible to noise.
Further, with reference to FIG. 5, when the reproduction device of a recording medium is configured by a system LSI, in addition to the servo controller 50, a microprocessor 51, and a digital signal processor (DSP) 52 are formed on a single semiconductor chip 60. In this case, the noise of the microprocessor 51 is increased, due to being mixed with the analog signals (IN, SG1, SG2, SG3) of the servo controller 50. Thus, it is difficult to incorporate the servo controller 50 in the system LSI.
It is a first object of the present invention to provide a servo controller and a servo control method that provides the reading of servo data recorded on a servo section of a recording medium and compresses the servo section to increase the amount of recording data.
It is a second object of the present invention to provide a phase calculator and a method for calculating a phase that are adaptable to a high frequency input signal of the recording medium and decrease the effects resulting from noise.
To achieve the above objects, the present invention provides a servo controller for correcting a read position of a read head that reads data recorded on a recording medium. A servo section is defined on the recording medium. The servo section includes a plurality of segments. The servo controller includes an automatic gain control (AGC) circuit for generating an amplified data signal having a predetermined amplitude from data signals that have different amplitudes and are read from the segments of the servo section. The amplified data signal is generated in accordance with a predetermined AGC voltage to generate an amplified data signal having a predetermined amplitude. A filter circuit is connected to the AGC circuit. The filter circuit eliminates unnecessary frequency elements from the amplified data signal to generate a filtered data signal. An A/D converter is connected to the filter circuit. The A/D converter converts the filtered data signal to a digital data signal. An AGC circuit controller is connected to the A/D converter. The AGC circuit controller generates an AGC signal to control the gain of the AGC circuit in accordance with the digital data signal. A D/A converter is connected to the AGC circuit controller. The D/A converter converts the AGC signal to an analog signal so to generate an AGC voltage, which is supplied to the AGC circuit. The AGC circuit controller generates the AGC signal corresponding to the next segment in accordance with an amplification ratio between the data signals read from each of the segments of the servo section, before reading the next segment.
The present invention further provides a servo controller for correcting a read position of a read head that reads data recorded on a recording medium. A servo section is defined on the recording medium. The servo section includes an R/W recovery segment, a servo mark segment, an AGC segment, and a phase detection segment. The servo controller includes an AGC circuit for generating an amplified data signal having a predetermined amplitude from data signals that have different amplitudes and are read from the R/W recovery segment, the servo mark segment, the AGC segment, and the phase detection segment. The amplified data signal is generated in accordance with an AGC voltage. A filter circuit is connected to the AGC circuit. The filter circuit eliminates unnecessary frequency elements from the amplified data signal to generate a filtered data signal. An A/D converter is connected to the filter circuit. The A/D converter converts the filtered data signal to a digital data signal. An AGC circuit controller is connected to the A/D-converter. The AGC circuit controller generates an AGC signal to control the gain of the AGC circuit in accordance with the digital data signal. A D/A converter is connected to the AGC circuit controller. The D/A converter converts the AGC signal to an analog signal to generate an AGC voltage, which is supplied to the AGC circuit. The AGC circuit controller generates the AGC signal corresponding to one of the AGC segment and the phase detection segment in accordance with an amplitude ratio between an amplitude of a first data signal, which is read from the R/W recovery segment, and an amplitude of a second data signal, which is read from one of the AGC segment and the phase detection segment, before reading the one of the AGC segment and the phase detection segment.
The present invention further provides a first servo control method for correcting a read position of a read head that reads data recorded on a recording medium. A servo section is defined on the recording medium. The servo section includes an R/W recovery segment, a servo mark segment, an AGC segment, and a phase detection segment. The method includes generating an amplified data signal having a predetermined amplitude from data signals that have different amplitudes and are read from the R/W recovery segment, the servo mark segment, the AGC segment, and the phase detection segment. The amplified data signal is generated in accordance with an AGC voltage. The method further includes generating a filtered data signal by eliminating unnecessary frequency elements from the amplified data signal, generating a digital data signal by A/D converting the filtered data signal, generating an AGC signal to control the gain of the AGC circuit in accordance with the digital data signal, and generating the AGC voltage by converting the AGC signal to an analog signal. The AGC signal generating step includes generating the AGC signal corresponding to one of the AGC segment and the phase detection segment in accordance with an amplitude ratio between an amplitude of a first data signal, which is read from the R/W recovery segment, and an amplitude of a second data signal, which is read from one of the AGC segment and the phase detection segment, before reading the one of the AGC segment and the phase detection segment.
The present invention further provides a second servo control method for correcting a read position of a read head that reads data recorded on a recording medium. A servo section is defined on the recording medium. The servo section includes an R/W recovery segment, a servo mark segment, an AGC segment, and a phase detection segment. The method includes generating an amplified data signal having a predetermined amplitude from data signals that have different amplitudes and are read from the R/W recovery segment, the servo mark segment, the AGC segment, and the phase detection segment. The amplified data signal is generated in accordance with an AGC voltage. The method further includes generating a filtered data signal by eliminating unnecessary frequency elements from the amplified data signal, generating a digital data signal by A/D converting the filtered data signal, generating an AGC signal to control the gain of the AGC circuit in accordance with the digital data signal, and generating the AGC voltage by converting the AGC signal to an analog signal. The AGC signal generating step includes storing a first AGC signal when the AGC voltage converges to a predetermined value during the reading of the R/W recovery segment and storing a second AGC signal when the AGC control voltage converges to a predetermined value during the reading of the AGC segment. The AGC generating step also includes generating the AGC signal in correspondence with at least one of the AGC segment and the phase detection segment, before reading the at least one of the AGC segment and the phase detection segment with a firmware in accordance with the stored first and second AGC signals.
The present invention further provides a first method for calculating a phase of a signal. The method includes generating an amplified input signal, which includes a fundamental wave of an input signal, by amplifying the input signal with a high gain, and converting the amplified input signal to a multiple-value digital signal using at least one determination level. The determination level is lower than the peak of the amplified input signal. The method further includes calculating the phase of the fundamental wave of the input signal using the digital signal.
The present invention further provides a second method for calculating a phase of a signal. The method includes generating an amplified input signal, which includes a fundamental wave of an input signal, by amplifying the input signal with a high gain. The amplitude of the amplified input signal is greater than a predetermined determination range. The method further includes converting the amplified input signal to a digital signal having at least two-values in accordance with the determination range, and calculating the phase of the fundamental wave of the input signal using the digital signal.
The present invention further provides a phase calculator for calculating a phase of a signal. The phase calculator includes an amplifier for generating an amplified input signal, which includes a fundamental wave of an input signal, by amplifying the input signal with a predetermined gain. A comparator is connected to the amplifier. The comparator compares at least one determination level with the amplified input signal to generate a determination signal having a digital data string that includes two or more values. A phase calculation circuit is connected to the comparator. The phase calculation circuit calculates the phase of the input signal in accordance with the determination signal. The determination level includes a maximum value and a minimum value. The predetermined gain of the amplifier is set such that the amplitude of the amplified input signal exceeds the maximum and minimum values of the determination level.
The present invention further provides an alternative phase calculator for calculating a phase of a signal. The phase calculator includes an amplifier for generating an amplified input signal, which includes a fundamental wave of an input signal, by amplifying the input signal with a predetermined gain. A comparator is connected to the amplifier. The comparator compares the amplified input signal with a predetermined input range to generate a determination signal having a digital data string that includes two or more values. A phase calculation circuit is connected to the comparator. The phase calculation circuit calculates the phase of the input signal in accordance with the determination signal. The gain of the amplifier is set so that the amplitude of the amplified input signal is excluded from the input range.
The present invention further provides a method for testing a phase calculator. The phase calculator amplifies an input signal with a predetermined gain to generate an amplified input signal; compares the amplified input signal with at least one determination level; generates a digital data string having two or more values; and calculates a phase of the input signal with the digital data string. The testing method includes connecting a digital signal generator, which generates a rectangular wave, to the phase calculator, and providing the rectangular wave as the input signal to the phase calculator. The functions of the phase calculator are tested in accordance with the rectangular wave.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.